Ink jet printers and plotters are well known. The print quality of these printers is dependent on the consistent, successful functioning of the ink jet print heads which are susceptible to clogging and failure over time. To overcome the problems with deterioration of ink jet print heads over time, it is necessary to periodically replace the print heads. Early solutions to this problem replaced only the print head, as shown, for example, in U.S. Pat. No. 4,074,284. More recently, disposable ink jet cartridges have been developed to solve this problem, as described, for example, in U.S. Pat. Nos. 4,500,895, 4,931,811, 4,931,812 and 5,182,579.
Disposable ink jet cartridges of this type are designed to operate for a useful life such that the head elements will function a very high percentage of the time (e.g., 99% of the time) during the life of the disposable cartridge. To ensure that this demanding performance figure is maintained, conventional disposable ink jet cartridges have a predetermined amount of ink contained within the cartridge that is available to be dispensed through the print head. The maximum amount of ink that is contained in the disposable cartridge is a function of how much printing the print head elements can do before failing to function at the very high performance percentage. Once the predetermined amount of ink in the cartridge is used, the entire ink jet cartridge is discarded.
While the use of disposable cartridges has effectively guaranteed the print quality of ink jet printers at the failure rate dictated by the particular disposable cartridge, there are many print applications which could tolerate a higher potential failure rate in exchange for an extended period of operation of the ink jet print head. Unfortunately, when existing disposable ink jet cartridges run out of ink, the print head is still functioning adequately in the vast majority of cases. Discarding ink jet cartridges that still have adequately functioning print heads wastes resources. In addition, frequent replacement of ink jet cartridges is time and labor intensive for large print applications. Consequently, many users have resorted to refilling ink jet cartridges in order to prolong the useful life of the print heads.
Manually refilling ink jet cartridges can be a messy and potentially hazardous operation that requires significant mechanical skill. To manually refill an ink jet cartridge, a user must access the original ink supply container in the ink jet cartridge and pump, pour, or otherwise force ink into that supply container. Accessing any of the ink couplings exposes the user to the ink and the ink to contamination. In addition, the user may inadvertently introduce air bubbles into the system which affects the flow of the ink and its ability to provide crisp, even print.
Automatic ink supply and refill systems for ink jet printers that do not use disposable ink jet cartridges typically are known. Automatic ink supply and refill systems can be classified either as passive refill systems which rely on gravitational or pressure differentials to cause the ink to flow through the system or active systems which uses some type of pump or mechanical assist to move the ink through the system.
Active ink refill systems have been used with either a continuous ink supply system, such as described in U.S. Pat. Nos. 4,399,446, 4,462,037 and 4,680,696, or an on-demand ink supply system, such as described in U.S. Pat. Nos. 4,074,284 and 4,432,005. The primary reason why these types of active ink refill systems are not useful for refilling a disposable ink jet cartridge is that these systems have print heads that rely on atmospheric or positive pressure hydrodynamic conditions to supply ink to the print nozzles. As such, it is typical that the ink refill system will have a feedback or outlet port on the print head to prevent the hydrodynamic condition of the print head from falling below atmospheric pressure.
Passive ink refill systems have used gravity to feed ink as controlled by a three way valve to feed ink from an ink reservoir to an ink supply container as part of a single replaceable unit that is carried by the print carriage, as described, for example, in U.S. Pat. No. 4,959,667. Early versions of this type of single replaceable unit ink delivery system are shown, for example, in U.S. Pat. Nos. 4,714,937 and 4,885,595. This method may be useful when the print heads are printing vertically and the ink reservoir can be positioned behind the print heads and above the ink supply container. When the print heads are printing on a large horizontal surface, however, the print head performance would be greatly diminished if the weight and volume of a large reservoir of ink would need to be supported by the print carriage as it traversed across the print medium.
For all of these reasons, almost all existing ink refill systems for use with disposable ink jet cartridges involve some type of service station which refills the ink jet cartridge only when the print carriage is at one or the other end of the print axis so that the ink jet cartridges can be docked with the service station. Once docked, the ink reservoir in the ink jet cartridge is quickly refilled and the print carriage is allowed to return to its printing operation. Various examples of service station-type ink refill systems for disposable ink jet cartridges are shown in U.S. Pat. Nos. 3,967,286, 4,967,207, 4,968,998, and 5,136,305.
There are two basic problems with service station-type ink refill systems. First, the print speed of the ink jet printer is decreased by the time required to perform the docking and refill operation. Second, and more importantly, in order to minimize the time of the docking and refill operation, the ink is quickly transferred to the ink jet cartridge at a pressure that typically exceeds the nominal hydrodynamic properties of the ink jet cartridge. As a result, there can be leaking or weeping of the print heads during the refill operation. The problems of leaking or weeping of ink are discussed, for example, in Ertuk, E., et al., "Ink Retention in a Color Thermal Inkjet Printer", Hewlett-Packard Journal, Aug. 1988, pp. 41-44.
While the use of disposable ink jet cartridges has significantly increased the print quality of ink jet printers, this increase in print quality has come at the expense of a significant waste of resources in the form of empty ink jet cartridges that still have long periods of usable life remaining for the print heads. Existing techniques to refill disposable ink jet cartridges suffer from numerous drawbacks. Consequently, an automatic ink refill system for disposable ink jet cartridges that improved on the existing techniques for refilling disposable ink jet cartridges would be greatly appreciated.